1. Field of the Invention
This invention relates to liquid level responsive apparatus and more particularly to such apparatus which detects a departure of the level of liquid in one or more containers from a predetermined level.
2. Description of the Prior Art
Various devices have heretofore been proposed employing a gas delivery tube for sensing a liquid level.
Cawley, et al., in U.S. Pat. No. 3,494,191, show a fluid driven surface level sensing system in which a level sensing element discharges a jet against the surface of liquid in a vessel. Many pneumatic dimension gaging devices operate in a similar manner to vary a back pressure or signal pressure in accordance with the spacing between a nozzle and a work piece in the path of the nozzle. The Cawley, et al. structure cannot be used with a plurality of containers.
Gauthier, et al., in U.S. Pat. No. 3,734,313, show a bulk bin level indicator in which a pneumatically operated sensor having a J-shaped output tube supplies air to an input tube which may be obstructed by bulk material present at that level, a pressure change at the input tube occurring when there is no material present and providing a signal at a pressure operated switch. The Gauthier, et al. structure cannot be used with a plurality of containers.
Cascio, in U.S. Pat. No. 3,885,435 shows a method and device for detecting presence or absence of a fluid in a receptacle, in which a detecting device is employed having an expansible chamber for receiving the fluid and disposed within a passageway. An air supply is connected through a pressure regulator to the passageway which is also connected to a fluidic switch, access of air to the switch being determined by the condition of the expansible chamber. In this construction, unlike those previously mentioned, the air is kept out of contact with the liquid the level of which is to be sensed so that there is no contamination or chemical combination of the air with the liquid. The Cascio structure cannot be used with a plurality of containers.
Kalle, in U.S. Pat. No. 3,137,137 shows a regulator in which a bubble tube extends downwardly into a liquid container, the tube being supplied with pressure gas from a source through a restriction. A branch conduit extends from the bubble tube to an impulse transmitting mechanism which includes a flexible diaphragm to provide a signal for control purposes. The use of a bubble tube subjects the liquid to possibility of contamination or oxidation which is objectionable with many chemical solutions whose level is to be sensed. The Kalle structure cannot be used with a plurality of containers.